Abstract/Summary

At the heart of diversity lies evolution, a continually acting process that has shaped and honed the enormous variety of life forms on Earth. To study evolutionary tempos and modes at a high resolution this thesis uses ancestral state reconstruction. This powerful, statistical method works within the framework of a novel, phylogenetic model which flexibly embraces the temporal and taxonomic complexity of the evolutionary process. Consistently across geographical and morphological data covering a wide range of species from dinosaurs to angiosperms to fish, evolutionary mode is broadly characterised by an overwhelming majority of negligible and small sized changes, interspersed with comparatively rare, exceptionally large ones. However, importantly, evolution is shown to work on a continuous scale without such categorical distinction. At a finer level, the magnitude of evolution’s steps differs depending on the direction of change being selected for, organisms’ biological history and the environment an organism evolves in. Changes to morphology of an exceptional magnitude have contributed to the process of undergoing major evolutionary transitions such as those seen in cetaceans and bats. These exceptional changes also differentially affect speciation and body size evolution depending on the nature of an organism’s environment. The signatures of evolutionary and ecological processes through time are revealed, for the first time showing that global scale movement across a famous evolutionary radiation universally follows an early burst pattern, moderated by speciation. On a larger temporal and taxonomic scale evolutionary changes increase in magnitude constantly through time suggesting that despite physical space filling up, there is no limit to evolutionary potential or to the diversity it creates. Current results spanning varying scales are viewed in the light of historical concepts of adaptive landscapes with leaps between and within peaks and zones, and are reconciled within the framework of this complex biological paradigm.